SCEC Award Number 14045 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Seismicity, Swarms, and Strain Changes in Southern California
Investigator(s)
Name Organization
Peter Shearer University of California, San Diego
Other Participants Graduate student (to be named)
SCEC Priorities 2b, 2c, 5d SCEC Groups Geodesy, EFP, Seismology
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 This SCEC funded research involves continued analysis of earthquakes recorded by the Southern California Seismic Network (SCSN). This has led to greatly improved earthquake locations, focal mechanisms, and estimates of stress drop. We are now using these products to perform integrated studies of seismicity and address a number of issues related to seismic hazard. We have recently focused on studying earthquake triggering models and their relationship to swarms and foreshock sequences. We have identified several aspects of the space/time clustering of seismicity that cannot be explained with standard (i.e., ETAS) triggering models, including details of the foreshock and aftershock behavior for small earthquakes. In particular, we have found that a significant fraction of small earthquake clustering is swarm-like and probably caused by underlying physical drivers, such as fluid flow or slow slip. We have now begun searching for correlations of seismicity with aseismic transients observed in geodetic data, in particular near the laser strainmeters at Piñon Flat Observatory (PFO) and surrounding borehole strainmeters from the Plate Boundary Observatory (PBO). We have identified at least ten examples where strain anomalies are associated with peaks in the local seismicity rate. Ongoing results of this work include a more detailed understanding of seismicity patterns and their relation to crustal deformation. This knowledge contributes to quantitative assessments of earthquake potential and seismic hazard in southern California.
Intellectual Merit Our research relates to many key SCEC objectives, including characterizing seismicity clustering and its implications for earthquake prediction. Our main contribution has been to systematically and objectively examine large amounts of earthquake data, including swarms and foreshock sequences, to test whether existing models of earthquake clustering are adequate to explain the observations.
Broader Impacts This project helped support graduate student Wei Wang. Our research will help quantify earthquake clustering and triggering in southern California, which has broad implications for earthquake forecasting and predictability. Advances in these areas would have clear societal benefits.
Exemplary Figure Figure 1. Seismicity on a portion of the San Jacinto fault, colored by year of occurrence (brown: 1980–1984, red: 1985–1989, yellow: 1990–1994, green: 1995–1999, cyan: 2000–2004; blue: 2005–2009, purple: 2010–2013. Earthquakes of M 4 and greater are shown as circles, with size proportional to magnitude. Locations are from the HYS catalog (Hauksson et al., 2012).
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